I'm still trying to determine an issue on my 2RZ. Now that it is colder out, a problem with hesitation has become more predominant. When the engine is cold, it starts just fine but as soon as I pull on the road, it has very little throttle response. I can push the pedal down 50% and she will move slightly faster than an idle speed. Other mornings, it drives without a single problem. The issue always goes away once the engine starts to warm up (actually, within 15-20 seconds the problem is gone). I figured the TPS might be at fault even though it's passed each time I've tested it when it's cold. I had planned to buy a new one anyways, until yesterday.

I pull out onto a main road and had forgotten about the possible hesitation. Of course, at the time the truck went no where. I pushed the pedal down to the floor and that is when I got two, loud, distinctive back fires up threw the intake manifold.

So this is my conclusion so far;
TPS shouldn't cause a backfire like that
A stretched Timing chain should cause the problem on every cold start.

The PCV hasn't been replaced. I'll do that today. Intake/Throttle body just got resealed during my hunt for this problem. I seafoamed the intake and engine and it's much cleaner but didn't change anything.
I also cleaned the Idle speed controller (highly recommended).